1. Field of the Invention
The present invention relates to linear fastener driving tools, and, more particularly, directed to portable tools that drive staples, nails, or other linearly driven fasteners. The invention is specifically disclosed as a gas spring linear fastener driving tool, in which a cylinder filled with compressed gas is used to quickly force a piston through a driving stroke movement, while also driving a fastener into a workpiece. The piston is then moved back to its starting position by use of a rotary-to-linear lifter, which again compresses the gas above the piston, thereby preparing the tool for another driving stroke. A driver member is attached to the piston, and has protrusions along its edges that are used to contact the lifter member, which lifts the driver during a return stroke. A pivotable latch is controlled to move into either an interfering position or a non-interfering position with respect to the driver protrusions, and acts as a safety device, by preventing the driver from making a full driving stroke at an improper time. In alternative embodiments, the fastener driving tool uses a different type of driving device, such as a mechanical spring, to force the driver into a driving stroke. In other alternative embodiments, the fastener driving tool includes a rotary-to-linear lifter having multiple protruding pins that lift the fastener driver element back to the initiating ready position, in which at least one of the lifter pins has a shape (or geometry) that reduces the side-loading forces between the lifter pin and the fastener driver element; and the fastener driving tool includes a movable latch that is controlled to disengage from a slotted rib (a raised wall with spaced-apart openings) along one side of the driver element during a driving stroke, but also will tend to engage the slotted rib of the driver element as a safety interlock.
2. Description of the Related Art
An early air spring fastener driving tool is disclosed in U.S. Pat. No. 4,215,808, to Sollberger. The Sollberger patent used a rack and pinion-type gear to “jack” the piston back to its driving position. A separate motor was to be attached to a belt that was worn by the user; a separate flexible mechanical cable was used to take the motor's mechanical output to the driving tool pinion gear, through a drive train.
Another air spring fastener driving tool is disclosed in U.S. Pat. No. 5,720,423, to Kondo. This Kondo patent used a separate air replenishing supply tank with an air replenishing piston to refresh the pressurized air needed to drive a piston that in turn drove a fastener into an object.
Another air spring fastener driving tool is disclosed in published patent application no. US2006/0180631, by Pedicini, which uses a rack and pinion to move the piston back to its driving position. The rack and pinion gear are decoupled during the drive stroke, and a sensor is used to detect this decoupling. The Pedicini tool uses a release valve to replenish the air that is lost between nail drives.
What is needed in the art is a portable fastener driving tool that is electrically powered, but which uses a gas spring principle of operation to drive a fastener into an object, and also uses few moving parts, which allows for simplicity of operation and provides a substantially gas-tight system for containing the pressurized gas for the gas spring.